1. Field of the Invention
The present invention relates to a power transfer device, a power supply device and a power receiving device.
2. Description of the Related Art
Recently, various electronic devices have been developed and mobile devices are also widely used. The mobile devices and some stationary devices incorporate batteries as a power source, and the batteries need to be charged by periodically receiving power supplied from the outside. The power supply method used can be roughly classified into, for example, a wired system and a wireless system. In the wired system, for example, a power supply terminal is electrically and directly connected to a terminal of a device to be charged, and power is supplied via this contact point. On the other hand, in the wireless system, for example, a transformer is used, and the device to be charged is electromagnetically coupled to a power supply device in a non-contact manner. Thus, power is supplied using an electric field or a magnetic field. There are many advantages to supplying power using the wireless system, for example, omitting the need to connect device terminals, and thus it Is being used in various devices.
When power is supplied by the wireless system, energy transfer efficiency of the transformer is important. For example, it is well known that the energy transfer efficiency of a transformer that has a coupling constant of 1 and that is coupled by em iron core hewing no magnetic flux leakage can foe made to be 1. The energy transfer efficiency of the transformer can be confirmed by a mathematical expression (refer to Japanese Patent Application Publication No. 2006-1238548, Electromagnetism Exercises p. 277 and p. 278, Kyoritsu Shuppan, and Annals of Physics, vol. 323, no. 1, pp. 34-38, Januray 2008, “Efficient Wireless non-radiative mid-range energy transfer”),